(1) Field of the Invention
To check the performance of an acoustic array, it is advisable to include a calibration circuit within the hydrophone channels for evaluating the gain and phase vs. frequency for a particular hydrophone channel as well as providing step gain control.
(2) Description of the Prior Art
Analog tonals of low distortion with absolute gain and phase are difficult to provide within the hydrophone preamplifier circuitry. Therefore, it is common practice to employ a hard clipped tonal. The clipped tonal presents a fundamental and all its odd harmonics. A hard clipped tonal does not provide a continuous gain and phase vs. frequency function. When processing data from a multi-element array, it is essential that the gain and phase vs. frequency are stable and maintained within specifications.